Practical Considerations when Reconditioning Overly Dry Soybeans

This fall harvest U.S. soybean farmers face multiple challenges. Export projections have dimmed on account of reduced sales to China. Prices continue to decline. Warm weather has been shrinking the soybean crop in the field in terms of moisture content. If projections hold, soybeans will likely be in storage for much longer than typical. This could be the beginning of a new normal. 

Economic Incentive

Soybeans are marketed based on a trade standard of 13% moisture content and a test weight of 60 pounds per bushel. At moisture contents above this level discounts are applied to sales but below this level sellers are missing the opportunity to have additional moisture weight included in their grain sale. 

The following example illustrates the economic incentive for reconditioning overly dry soybeans based on harvesting and storing 200 acres that yield 50 bu/ac with a moisture content of 9.5% and a sale price of $10/bu. Of the 50 bu/ac or 3,000 pounds per acre harvested, 90.5% or 2,715 pounds is dry matter. That is 45.25 bu/ac of the 50 bu/ac is dry matter while the remaining 285 pounds per acre or 4.75 bu/ac is moisture. If the moisture content could be increased to 11.5% or 13% that would equate to an additional 1.13 bu/ac or 2.01 bu/ac, respectively. The cost of electricity to operate a fan is the primary expense of hydrating. For this example assume 10,000 bu of soybeans are harvested and placed in a single 10,000 bu bin set up to provide airflow similar to natural air drying of corn (i.e., about 1 CFM/bu). With electricity costs of $0.10/kWh and a 10 kW fan running for 1,000 hours through the conditioning process, the cost would be $1,000 for the whole 200 ac. Additional revenue after conditioning to 11.5% or 13% would be $2,260 or $4,023, respectively. After deducting the $1,000 cost, the net return would be $1,260 or $3,023, respectively. On a per acre basis, that is $6.30/ac when reconditioning to 11.5% and $15.12/ac when reconditioning to 13%. Alternatively, if the same fan were operated the same amount of time and reconditioning only increased moisture content from 9.5% to 10% the net return would have been a net loss of $444 or $2.22/ac because the additional revenue for the 0.5 percentage point of increase in moisture content would have only been $556. 

The above example illustrates the economic incentive to recondition soybeans but a net profit may not always be achieved. The additional revenue generated from moisture gained is relatively straightforward but the cost to accomplish the conditioning effect depends on the specific aeration system and electrical cost, weather conditions, and management of the fan run cycles. 

Technical Feasibility and Cautions

Reconditioning overly dry soybeans successfully was demonstrated by researchers at Purdue University in the early 2000s (Maier & Montross, 2002[1]). They concluded that “reconditioning soybeans using aeration and an automatic fan controller is technically and economically feasible. For the scenarios evaluated, average net economic gains varied from 0.051 to $0.43/bu when reconditioning 10% soybeans. The ability to recondition is dependent on location. The Western Corn Belt is less conducive to reconditioning than the Eastern Corn Belt. The average moisture content increase in soybeans was 0.5 to 0.6 percentage points less at low airflow rates for Des Moines than for Indianapolis. Large yearly variations are to be expected in the net economic gain when reconditioning soybeans. In Indianapolis, the average net gain varied from 0.08 to $0.193/bu in soybeans over twenty-nine years in the farm bin with only a single unload and low airflow. A shallower bin is more economical for reconditioning than a deeper tank because greater grain depths require disproportionately higher horsepower fans to achieve the same airflow rate, which negatively affect the net gain.” They also cautioned about the potential for spoilage “especially when conditioning extends into the late spring and early summer period. In the examples explored, safe storage moistures were generally exceeded in the upper grain layers and fairly significant gradients developed within the bin. Stirring machines in on-farm bins are a tool that could be used to achieve better moisture uniformity during conditioning. This would also avoid the need to reverse the airflow in push aeration systems. Another physical challenge (and safety concern) of soybean conditioning is leveling grain surfaces especially in larger diameter bins. The complexity of the automatic controller needs to be fully understood by the operator. Setting limits for the programmable variables can create an operational window that can be too narrow or too wide. The reliability of an automatic fan controller also should be considered. Air temperature and humidity sensors must be regularly checked for accuracy, and calibration procedures should be carefully followed.”

An additional concern mentioned by Hellevang (2023[2]), is the expansion in volume as low-moisture soybeans absorb moisture during reconditioning. This will pack them tighter into the bin and can add pressure on the sidewalls. In the most extreme case, this could damage the bin’s bolted connections including foundation anchors or even rupture a bin wall along a bolted seam due to the increased pressure on the wall. A mitigation strategy when moisture content increases by more than a couple percentage points is to draw a core by unloading some beans which will relieve some of the increased pressure. Or, if beans are being reconditioned in a bin with a stirring system, another option would be to run the stirrers intermittently and mix the layers and average moisture contents. 

Air-Moisture Equilibrium Relationship

Soybeans can be reconditioned by operating aeration fans during periods with the desired air temperature and relative humidity (RH). Conditioning requires high airflow rates for several weeks using air with an average relative humidity above 63.5% to condition soybeans to 12-13% when ambient temperatures range between 45 and 70°F (Table 1). At lower temperatures, air holds less humidity and little conditioning occurs. Be aware that the air will be heated 3 to 5 degrees as it goes through the fan, which reduces the air relative humidity 3-4 percentage points for each degree of heating. 

A reconditioning zone develops and moves slowly through the grain mass in the direction of airflow like a drying zone in natural-air drying. Conditioning occurs fastest when airflow rate, cubic feet of airflow per minute per bushel (CFM/bu), is high and air is warm and humid. 

Table 2 was developed using the ISU Grain Aeration & Storage App (available free of charge for Android and I-phones) which allows determination of the Equilibrium Moisture Content (EMC) relationship for soybeans (and more than a dozen other crops) as a function of ambient temperature and relative humidity. It is important to note that no matter the initial temperature or moisture content of soybeans, when aerated with air at 50°F and 60% RH, they will equilibrate to 11.2% moisture content. At 70% RH, they will equilibrate to 13.2% and at 80% to 15.6%. At 40°F, soybeans will equilibrate to 11.5% at 60% RH, 13.5% at 70% RH and 15.9% at 80% RH.

Reconditioning Approaches

There are at least four approaches farmers and elevator managers can consider: (1) standard bin set-up with updraft aeration, (2) modified bin set-up with downdraft aeration, (3) modified bin set-up with a STIG DRI-Stack®System, and (4) standard bin set-up with updraft aeration and a stirring system. 

A simple thermostat suffices to cool soybeans below a target temperature of 50°F, for example. However, when soybeans are to be reconditioned, an automatic control system that operates fans based on temperature and relative humidity is preferred over an older style humidistat. Technology platforms such as the AGI Suretrack, Amber Ag ACE Air, OPI Blue, STIG Auto-Bin, or Sukup Synk system are commercially available and highly recommended.

1. Updraft Aeration

Recent research undertaken by Lawrence et al. (2025[3]) using a computer simulation model and six years of weather data are summarized in Table 3. Fans were assumed to push air up through the grain mass and operate whenever the air-EMC was 12% or higher but not above 80% RH. The results indicate that higher airflow rates and longer conditioning periods resulted in higher average moisture contents, i.e., 11.1 to 12.1% compared to 10.5 to 10.9% with airflow rates of 0.75 CFM/bu versus 0.29 CFM/bu, respectively. About half of the moisture gain occurred between October 1 and November 14 (6 weeks), i.e., 0.5, 0.8 and 1.1 percentage points (PPTs), compared to an additional 0.4, 0.7 and 1.0 PPTs between November 15 and March 30 (14 weeks). Interestingly, maximum moisture content achieved ranged from 13.8 to 14.1% and was independent of airflow rate and reconditioning period. 

Results summarized in Table 4 indicate the greatest net gain occurs when soybeans are reconditioned at the highest airflow rate under Arkansas weather conditions (14.8 to 24.2 cents/bu) followed by Iowa (9.1 to 17.5 cents/bu) and North Dakota (4.5 to 5.3 cents/bu). Net gain at about a third of the airflow rate (0.29 CFM/bu) was about 5 times lower in North Dakota compared to 2.5 times lower in Iowa and 1.5 times lower in Arkansas.
 

2. Downdraft Aeration

One of the limitations of updraft aeration is the reconditioning of soybeans from the bottom-up which can result in a substantial moisture gradient because the slowly moving conditioning front may not reach the upper layers. Past research from Purdue University (Maier & Montross, 2002) investigated the potential of down-draft aeration. Results indicate the greatest reconditioning potential can be achieved with that approach combined with higher airflow rate, and multiple last-in, first-out unloading cycles (Table 5). For Des Moines conditions, an airflow rate of 0.22 CFM/bu resulted in an average moisture content gain of 2.3, 2.1 and 2.0 PPTs compared to 0.8, 0.8 and 1.0 PPTs at 0.11 CFM/bu. Interestingly, the range of moisture content and standard deviations were similar for the unload schedules and respective airflow rates. Net gain in terms of $/bu were about 2.5 times greater at the higher airflow rate.

3. Targeted Layer Aeration

A recent innovation provides another potential approach for overcoming the limitations of updraft aeration. A modified bin set-up with a STIG[4] DRI-Stack®System system is an intriguing design directing airflow from the perforated floor through strategically placed stacks to targeted layers of a grain mass. However, no research results have been published with respect to soybean reconditioning but hopefully there will be in the near future. 

4. Updraft Aeration and Stirring

A third approach to overcome the non-uniformity of reconditioning in a bin set-up with updraft aeration, is stirring soybeans intermittently. Some have raised the concern that stirring will cause beans to split. That may perhaps be true if stirring machines are run continuously although no evidence has been presented in the past to support that concern. When reconditioning soybeans, they only need to be stirred intermittently perhaps every other week or once a month depending on the progress of the moisture front. 

At the ISU Kent Feed Mill & Grain Science Complex, we placed soybeans into a high airflow bin with updraft aeration and a stirring system on October 5. Soybeans averaged 8.8 to 9.7% moisture content with test weight of 56.8 to 58.1 lb/bu and 3.36 to 9.66% splits and 0 to 0.64% foreign material. The AGI Suretrack system was set to operate within an ambient temperature range of 50-68°F and a minimum air-EMC of 12%. Based on the EMC relationship shown in Table 1, RH will need to be at least 64.5% at 50°F and 66.5% at 65°F before the fans are turned on. During the past two weeks, the soybeans have reached 10.7% moisture in the bottom layer and 9.7% in the middle layer. The top layer remains at 9.0% moisture content after 129.5 hours of conditioning time. We plan to stir the layers after the first two weeks of conditioning. Results will be published once the trial is complete.

Summary

Reconditioning soybeans using aeration fans and an automatic controller is technically feasible and economically desirable. Reconditioning to a market moisture content of 13% depends on several variables. The Western Corn Belt is less conducive to reconditioning than the Eastern Corn Belt. The South-Central region of the U.S. is substantially more conducive than the North Central region. Higher airflow rates that take advantage of shorter periods of suitable air conditions can result in 0.5 to 1 PPTs increase of average moisture content between early October and mid-November in most years. Net economic gain when reconditioning soybeans also depends on aeration fan electricity costs and consumption. Doubling the down-draft airflow rate in a 60 ft diameter bin resulted in a 2.5 times higher net gain when reconditioned soybeans were unloaded every other month according to the last-in, first-out principle. A shallower bin is more economical for reconditioning than a deeper tank because greater grain depths require disproportionately higher horsepower fans to achieve the same airflow rate. This negatively affects the net gain. 

Storing soybeans longer than in the past may well become the new normal. In addition to the reasons mentioned above, U.S. demand for soybeans is shifting away from exports and toward domestic biofuels demand. The current renewable diesel boom has made the soybean oil share of the value of crush output larger and more volatile. In 2025, oil prices rose as meal prices fell (Janzen and Wang, 2025[5]). Given that soybeans are marketed based on 13% moisture content, producers have every incentive to harvest soybeans as close to 13% as feasible or to recondition soybeans harvested at lower moisture contents to maximize their return. The technology platforms and best practices are available to help them achieve their objective though additional research is needed to optimize the reconditioning process.

[1] Maier, D.E. and Montross, M.D. 2002. Reconditioning Overly Dry Soybeans. Grain Quality Fact Sheet #48, Purdue University.

[2] https://www.ndsu.edu/agriculture/ag-hub/ag-topics/crop-production/drying-storage/considerations-when-conditioning-too-dry-soybeans

[3] Lawrence, J., Obeng-Akrofi, G., Maier, D.E. 2025. Quantification of Soybean Hydration based on Grain Depth and Airflow Rate using Ambient Air. Oral presentation, ASABE AIM July 15, 2025. 

[4] https://cdn.prod.website-files.com/6373aea400cebcab9d1d626c/676040a9c8a1b0bbb876bd5d_Dri-Stack_Brochure_11.14.24_V4_small.pdf

[5] https://www.agriculture.com/partners-the-soybean-industry-response-to-t…